The present invention relates to a harmonic rejection design, and more particularly, to a phase-rotated harmonic-rejection mixer apparatus.
Increasing demand for transceiver devices with small form factors has motivated research on highly integrated low-cost transmitter and receiver circuits. For example, direct conversion transmitter (TX) and receiver (RX) circuits can simplify the signal path by using one up-conversion mixer to translate a baseband (BB) signal to a radio-frequency (RF) signal through a local oscillator (LO) signal and using one down-conversion mixer to translate an RF signal to a BB signal through an LO signal. However, due to the increasing demand for a larger signal bandwidth, the counter intermodulation products (CIM) become important in the transceiver design, especially the 3rd-order counter intermodulation product CIM3. One contributor to CIM3 (e.g., LO-3BB) comes from the baseband 3rd-order nonlinearity. For example, in the TX mixer, the 3rd harmonic of the baseband signal (i.e., 3BB) is up-converted to LO-3BB. Another contributor to CIM3 comes from the mixer, where up-conversion with the 3rd harmonic of the LO signal (i.e., 3LO) creates a signal component at 3LO-BB that can generate CIM3 (e.g., LO-3BB) due to intermodulation with a wanted signal (e.g., LO+BB) in a nonlinear amplifier. Hence, there is a need for an innovative mixer design which can effectively mitigate or cancel the undesired counter intermodulation products, especially the 3rd-order counter intermodulation product CIM3.